Power line communications (PLC) carry data on a conductor that is also used simultaneously for alternating current (AC) electrical power transmission (electric power distribution) to consumers. PLC can also be used on direct current (DC) systems, such as vehicle power, solar cell systems, or the like. PLC is sometimes also known as power line carrier, power line digital subscriber line (PDSL), mains communications, power line telecom (PLT), power line networking (PLN) and broadband over power lines (BPL). AC electrical power supply is also referred to as mains electricity, household power, household electricity, house current, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power. PLC systems typically operate by impressing a modulated carrier signal on the wiring system. Different types of PLC systems use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power distribution system was originally intended for transmission of AC power at typical frequencies of 50 or 60 Hz, some power wire circuits may have a limited ability to carry higher frequencies.
A switched-mode power supply (SMPS), also referred to as switching-mode power supply or switcher, is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics. An SMPS is usually employed to efficiently provide a regulated output voltage, typically at a level different from the input voltage. The pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which may minimize wasted energy. Ideally, a switched-mode power supply dissipates no power. Voltage regulation is typically achieved by varying the ratio of on-to-off time.
Typically, a power line modem (PLM) is used for communications over power lines. Like ordinary modems, a PLM is able to convert a binary data stream into a sequence of signals with predefined characteristics, such as frequency, levels, etc.), and vice-versa, the PLM is able to convert a sequence of signals back to a binary data stream.
The noise created by switching power supplies can cause problems for simple power line communications schemes. This is a particular problem in equipment that contains a SMPS and communicates using PLC over the same power connection.
Many switching power supplies make use of high frequency energy in the region of 50 kHz˜200 kHz. Power line modems also may use the same frequency range for PLC transmissions. When a piece of equipment uses both a SMPS and a power line modem, coexistence is a problem due to interference. This interference may occur both locally and between devices joined by a common power connection. Conventional solutions separate the power supply unit (PSU) block and the PLC block and isolate these blocks using suitable filtering to reduce the noise created by switching power supplies.